I been thinking of investing in a proball diff for my rusty, has anyone tried them? Are they worth it?

for bashing not really, for racing yes. you need to take it apart regularly for maintenance...

do you have a resonator pipe or something similar yet? imho i would invest in one of those 1st...

I actually have the pro 15 with a stinger. I have it running a lot better than your normal rusty tho.